1. Field of the Invention
The present invention relates to isocyanurate-modified polymethylene polyphenylene polyisocyanate compositions and to foams prepared from said polyisocyanate compositions. More particularly, the invention relates to polyisocyanate compositions containing from 15 to 50 weight percent isocyanurate content and to polyurethane isocyanurate foams prepared by reacting these compositions with oxyethylated polyols.
2. Description of the Prior Art
The prior art generally teaches the preparation of isocyanurate-modified isocyanate products, employing a variety of catalysts. U.S. Pat. No. 3,996,223 teaches a process for the preparation of polyurethane quasi-prepolymers containing isocyanurate structures by polymerization in the presence of catalytic quantites of a mixture of Mannich bases and carbamic acid esters prepared from isocyanates and alcohols containing secondary alcohol groups. U.S. Pat. No. 3,645,979 teaches the polymerization of an aromatic polyisocyanate and an aliphatic polyisocyanate in the presence of an organic phosphine catalyst. U.S. Pat. No. 3,652,424 teaches a process for the preparation of polyisocyanate compositions containing 5 to 19 percent by weight of toluene diisocyanate trimer by employing as trimerization catalysts substituted guanidines and isobiguanidines.
U.S. Pat. No. 3,723,363 teaches the preparation of polyurethane products by reacting a trimerized crude polyisocyanate having a functionality of at least 1.5 and preferably at least 3 with an isocyanurate content of 2 to 12 percent with various polyols. It further teaches that the preferred polyols are obtained by oxypropylating polyhydroxy compounds such as sucrose, sorbitol, glycerine, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol or mixtures thereof.